Today, the usage and differences of printf(), sprintf(), scanf() and sscanf() in C language have been analyzed and introduced in detail. Friends who need it can refer to it.
1、printf
grammar:
#include
int printf( const char *format, ... );
The printf() function prints output to STDOUT (standard output) and other parameters according to the format given by format. The return value is the number of characters output.
2、sprintf
grammar:
#include
int sprintf( char *buffer, const char *format, ... );
The sprintf() function is similar to printf(), and the format control is exactly the same. As long as it is a format string used by printf, it can be used in sprintf, but the output is sent to the buffer. The return value is the number of characters written.
Function 1: Format a string of numbers
sprintf(s, "%-8X", 12345); //s becomes: "12345"
The uppercase "X" represents the uppercase hexadecimal form, and the width occupies 8 positions, and the "-" represents left-justified.
Function 2: Control the printing format of floating-point numbers
Floating-point numbers are controlled by the format character "%f", and 6 digits after the decimal point are reserved by default. %m.nf" format, where m represents the width of printing, and n represents the number of digits after the decimal point
sprintf(s, "%10.3f", 3.1415626); //s变成：" 3.142"
Function 3: Connect two strings
direct connection:
char dest [256];
char src1[] = {'a','b','c','d','e'};
char src2[] ={'1','2','3','4'};s
printf(dest,"%.5s%.4s",src1,src2); //output:“abcde1234”
Intercept some characters of the string for connection,
char dest [256];
char src1[] = {'a','b','c','d','e'};
char src2[] ={'1','2','3','4'};
sprintf(dest,"%.*s%.*s",2,src1,3,src2); //output:“ab123”
Function 4: Character/Ascii code comparison
We know that if you print a character with "%d" or "%x", you can get its decimal or hexadecimal ASCII code; conversely, use "%c" to print an integer and you can see It corresponds to the ASCII character. The following program segment prints the ASCII code comparison table of all visible characters on the screen (printf is used here, note that when "#" and "%X" are used together, the hexadecimal number is automatically prefixed with "0X"):
for(int i = 32; i < 127; i++) {
printf("[ %c ]: %3d 0x%#04X\n", i, i, i);
}
Function 5: Print address information
Sometimes when debugging a program, we may want to check the addresses of certain variables or members. Since the address or pointer is only a 32-bit number, you can use the "%u" that prints unsigned integers to print them out:
sprintf(s, "%u", &i);
But usually people still like to use hexadecimal instead of decimal to display an address:
sprintf(s, "%08X", &i);
However, these are all indirect methods. For address printing, sprintf provides a special "%p":
sprintf(s, "%p", &i);
I think it is actually equivalent to:
sprintf(s, "%0*x", 2 * sizeof(void *), &i);
Function 6: Use the return value
The return value of printf and sprintf is the number of characters written.
That is to say, after each sprinf call ends, you do not need to call strlen again to know the length of the result string. Such as:
int len = sprintf(s, "%d", i);
3、scanf
grammar:
#include
int scanf( const char *format, ... );
The scanf() function reads from stdin (standard input) according to the format specified by format (format) and saves the data to other parameters.
4、sscanf
grammar:
#include
int sscanf( const char *buffer, const char *format, ... );
The function sscanf() is similar to scanf(), except that the input is read from the buffer.
sscanf is similar to scanf, both are used for input, except that the latter uses the screen (stdin) as the input source, and the former uses a fixed string as the input source
usage:
%[] means to read a character set, if the first character after [is "^", it means the opposite. The character string in [] can consist of 1 or more characters. The empty character set (%[]) is against the regulations and can lead to unpredictable results. %[^] is also against the regulations.
%[az] Read the string between az and stop if it is not before, such as
char s[]="hello, my friend"; // Note:, the comma is not between az
sscanf( s, “%[a-z]”, string ) ; // string=hello
%[^az] Read the character string not between az, and stop if it touches the character between az, such as
char s[]="HELLOkitty"; // Note:, the comma is not between az
sscanf( s, “%[^a-z]”, string ) ; // string=HELLO
%*[^=] preceded by * means that the variable is not saved. Skip qualified strings.
char s[]="notepad=1.0.0.1001" ;
char szfilename [32] = "" ;
int i = sscanf( s, "%*[^=]", szfilename) ;// szfilename=NULL, because it is not saved
intj = sscanf( s, "%*[^=]=%s", szfilename ) ;// szfilename=1.0.0.1001
%40c read 40 characters
%[^=] Read the string until it hits the'=' sign, there can be more characters after the'^', such as:
char s[]="notepad=1.0.0.1001" ;
char szfilename [32] = "" ;
int i = sscanf( s, "%[^=]", szfilename ) ; // szfilename=notepad
If the parameter format is: %[^=:], then notepad can also be read from notepad:1.0.0.1001.
The above is a detailed introduction about the usage and differences of printf(), sprintf(), scanf(), and sscanf(). I hope it will be helpful to your study.
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